How to texture paint large objects while retaining high quality paint
UV mapping is the way you can define how the faces of a 3d mesh are placed and projected in a 2d plane (texture).

You can increase, decrease, stretch the area in the UV mapping.

You can also attach a huge "image texture" to the mesh (UV mapping helps to map 3d mesh to 2d texture), so when you paint an object you won't loose any detail.

The bigger the texture is, the mode big the UV area should be

(in newest version of blender, you can have different UV MAP / texture with different pixel density --> check this article+video: new-udim-texture-painting, bu probabily you won't need it)

here you can check how different faces have different size as UV MAP